G 7 'een. — On Vegetable Ferments. 129 
of the changing substance.’ J. O’Sullivan also finds that the 
hydrolytic action of yeast at the ordinary temperature follows 
the same course as that of a simple chemical interchange, 
while its rate differs from that at which the alcoholic fermen- 
tation of yeast takes place. The fact that the action of the 
enzymes is always accompanied by an evolution of heat is 
also evidence to the same end. Lea 1 states, on the authority 
of Hoppe-Seyler and other observers, that the heat of 
combustion of the products of zymolysis is in all cases less 
than that of the substances from which they are derived. 
That we have to do then with an ordinary chemical 
reaction leading to hydration and subsequent decomposition, 
seems clear. What the exact nature of that reaction must 
still be largely a matter of hypothesis. The first thing that 
strikes an observer in this connection is the extremely small 
amount of the enzyme that is needed to bring about the 
transformation of an enormous amount of the body which it 
attacks. Thus O’Sullivan and Tompson 2 show in one of their 
experiments that a sample of invertase induced inversion of 
100,000 times its own weight of cane-sugar and that it was 
not destroyed or even injured by its action. This latter 
feature, which was first determined by Foster 3 in the case of 
salivary diastase, has been shown by many other observers to 
be characteristic of other enzymes. Based upon these two 
considerations we have the hypothesis that enzymic action 
may be similar to the action of nitric oxide in the manu- 
facture of sulphuric acid. Thus the ferment may be regarded 
as carrying water to the initial body by uniting with the 
latter, the combination now being capable of taking up water 
and being thereby decomposed. The resulting products may 
be only the hydrated body, or a number of bodies, while in 
all cases the decomposition liberates the enzyme unaltered. 
The decompositions we have seen are usually complex, 
diastase giving rise to various dextrins and maltose ; trypsin 
1 The Chemical Basis of the Animal Body, p. 75, 1892. 
2 op. cit. p. 927. 
3 M. Foster, On Amylolytic Ferments, Journ. Anat. and Phys., vol. I, 1867, p. 107. 
K 
